It was single player.. I went trough 4 different biomes now, in 5 separate caves.. non had animals or crystals.. I even checked in another save on the starting ylands cave and it's the same
I have been to 3 different yland cave systems,the longest one and the deepest one was the polar desert one.. there were no ylandium crystals or mutated animals in any of the cave systems and i cannot progress without ylandium dust